1. Technical Field of the Invention
The technology described herein relates generally to wireless communications and more particularly to circuits used to support wireless communications.
2. Description of Related Art
Communication systems are known to support wireless and wireline communications between wireless and/or wireline communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks to radio frequency identification (RFID) systems. Each type of communication system is constructed, and hence operates, in accordance with one or more communication standards. For instance, wireless communication systems may operate in accordance with one or more standards including, but not limited to, 3GPP, LTE, LTE Advanced, RFID, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), and/or variations thereof.
Depending on the type of wireless communication system, a wireless communication device, such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, RFID reader, RFID tag, et cetera communicates directly or indirectly with other wireless communication devices. For direct communications (also known as point-to-point communications), the participating wireless communication devices tune their receivers and transmitters to the same channel or channels (e.g., one of the plurality of radio frequency (RF) carriers of the wireless communication system) and communicate over that channel(s). For indirect wireless communications, each wireless communication device communicates directly with an associated base station (e.g., for cellular services) and/or an associated access point (e.g., for an in-home or in-building wireless network) via an assigned channel. To complete a communication connection between the wireless communication devices, the associated base stations and/or associated access points communicate with each other directly, via a system controller, via the public switch telephone network, via the Internet, and/or via some other wide area network.
For each wireless communication device to participate in wireless communications, it includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). As is known, the receiver is coupled to one or more antennas (e.g., MIMO) and may include one or more low noise amplifiers, one or more intermediate frequency stages, a filtering stage, and a data recovery stage. The low noise amplifier(s) receives inbound RF signals via the antenna and amplifies them. The one or more intermediate frequency stages mix the amplified RF signals with one or more local oscillations to convert the amplified RF signal into baseband signals or intermediate frequency (IF) signals. The filtering stage filters the baseband signals or the IF signals to attenuate unwanted out of band signals to produce filtered signals. The data recovery stage recovers raw data from the filtered signals in accordance with the particular wireless communication standard.
Currently, wireless communications occur within licensed or unlicensed frequency spectrums. For example, wireless local area network (WLAN) communications occur within the unlicensed Industrial, Scientific, and Medical (ISM) frequency spectrum of 900 MHz, 2.4 GHz, and 5 GHz.
Wireless transceivers implemented using integrated circuits (ICs) are designed to meet specific noise requirements. Two distinct versions of such transceivers are often manufactured, one with an internal transmitter/receiver (TR) switch and one designed to use an external TR switch. The latter version achieves better transmit and receive performance due to superiority of discrete external TR switches compared with integrated TR switches. As a result, a cost sensitive customer may opt for an integrated TR switch version, and a performance sensitive customer may choose an external TR switch version. Producing two versions increases mask costs and design verification time. In addition, it is known that transceivers with integrated TR switches suffer from degraded transmit and receive performance. The former is related to the additional load of the receiver, dissipating some of the transmit power. The latter is related to the additional load of the transmitter and TR switch, increasing the noise to the receiver.
Typically, two different versions of a transceiver IC are required in order to support an internal TR switch and external TR switch. Integrated inductors for these versions may need to be of different sizes in order to tune out differing amounts of capacitances present in the respective versions. The internal TR switch version may require additional resonating capacitance to correctly set the resonant frequency of the receive path during transmit mode. In addition, an external TR switch version may omit the TX series switch, in order to minimize transmit power losses.
FIG. 1 illustrates one example of a transceiver integrated circuit having an external TR switch where transceiver 100 includes transceiver IC 101, antenna 102 and external TR switch 103. Transceiver IC 101 transmits signals via transmitter 104 in connection with power amplifier (PA) 105 through output port 106. External transmit/receive (TR) switch 103, in transmit (TX mode), provides a connection between output port 106 and antenna 102 for signal transmission. During receive (RX) mode, signals are received through antenna 102 passing through external switch 103 and, in some configurations, through first low-noise amplifier (LNA) 107 and transceiver IC 101 via input port 108. Signals pass from input port 108 through integrated gate inductor 109 and second LNA 110 and ultimately receiver 111.
FIG. 2 illustrates one of many possible implementations for internal TR switches. Transceiver 200 includes antenna 201 connected to transceiver IC 202 via input/output port 203. Signals are transmitted from transceiver IC 202 to antenna 201 through transmitter 204 in connection with PA 205. PA 205 provides an amplified signal to TX series switch 206. In TX mode, TX series switch 206 is ON allowing amplified signals to pass through input/output port 203 to antenna 201. In addition, RX shunt switch 207 is ON (forming a low impedance path to ground). Internal gate inductor 208 resonates with the shunt capacitance in order that the receive path presents a high impedance to transmitter 204, thus minimizing power loss in that path. The size of RX shunt switch 207 is made sufficiently large that it does not limit the Q-factor of the resonant network, thus minimizing power dissipation in the switch. Also, it is made sufficiently large that during TX mode, when there are large voltages on input/output port 203 of transceiver IC 202, the voltage at LNA 209 input is small so that the voltage does not damage that input. Operating in reception mode, TX series switch 206 is in the off position in order to minimize loss of received signal power in the transmit path for transceiver 200. In addition, RX shunt switch 207 is off. Amplified signals are passed from LNA 209 to receiver 210.
Disadvantages of conventional approaches will be evident to one skilled in the art when presented in the disclosure that follows.